The present invention relates to a semiconductor device and more particularly to a semiconductor device with a specific resistance ratio between or among resistor elements formed on a semiconductor substrate.
A conventional semiconductor device is comprised of a semiconductor substrate (including a number of elements such as transistors, diodes, diffused resistors, and the like), and an insulation layer (referred to as a circuit wiring layer) for electrically wiring the elements. The circuit wiring layer is formed on the substrate in a given pattern of an insulating layer having contact holes formed at given locations. Contained in a number of the resistor elements formed on the substrate are two or more resistor elements requiring relative characteristics providing or satisfying a resistance ratio between or among the resistors. In order to obtain the relative characteristics required, the resistor elements of such type generally are located closely to one another, are about the same size, and extend in the same direction.
Even if those elements are thus formed, however, when circuit wiring layers cross a location on the insulation film on the substrate corresponding to the location of where the resistor elements are formed, stresses applied to the resistor element change. As a result, the relative characteristics of such resistor elements can not be kept.
A conventional semiconductor device with such a structure will be described referring to FIG. 1 through 3. Two P conductivity type resistor regions 14 and 16 constituting resistor elements are formed in an N conductivity substrate 12. Resistor elements 14 and 16 are disposed close to and in parallel with each other and are about the same size, in order to obtain a relative characteristic satisfying a resistance ratio 1:1 between these elements. The resistor element 14 is connected at both ends to circuit wiring layers 18 and 20. The resistor element 16 is also connected at both ends to circuit wires 22 and 24. An insulation layer 26 is formed on the substrate 12 except at the contact portions of the circuit wiring layers and the resistive elements. Another circuit wiring layer 28 for wiring other elements not shown is formed on the insulation substrate 26. The wiring layer 28 passes only resistor element 14, not the resistor element 16.
In a semiconductor device with such a structure, since the wiring layer 28 is partially formed at the location on the insulation layer 26 corresponding to the resistor element 14, the wiring layer 28 stresses the resistor element 14 to change the resistance of the resistor element 14. Therefore, the required relative characteristics of the resistor elements 14 and 16 can not be obtained even if the resistor elements 14 and 16 are formed in the close, parallel, and same size manner, as mentioned above. The phenomenon that the resistance of the resistor element formed in the semiconductor substrate changes when it is subjected to a stress is called a piezo-resistance effect. As the result of the piezo-resistive effect, the resistance of a P conductivity type resistor element formed on the (1 1 1) of a silicon substrate decreases. The resistance of the resistor element on the (1 0 0) surface exhibits a crystal-axis-dependent characteristic and changes dependent on the crystal axis.
Pure aluminum has been used for the circuit wiring layer. Recently, however, corrosion-resistive alloy such as Al-Si-Cu, Al-Si, and Al-Ti, poly silicon, or metal silicide have gradually been used. The circuit wiring layer made of such material applies to the substrate a larger stress than the circuit wiring layer made of the pure aluminum. Accordingly, in the conventional semiconductor device shown in FIGS. 1 to 3, when the circuit wiring layer 28 is made of the material as mentioned above, the piezo-resistance effect occuring in the resistor element 14 is greater, so that the relative characteristics of the resistor elements 14 and 16 are different from each other.